Microindentation fracture behavior of surface modified alumina ceramic using glass infiltration

This study investigates the effect of a low expansion glass (Mg3Al2Si6O18) treatment on the surface fracture toughness of sintered alumina. The surface fracture toughness was determined by direct indentation method (Vickers indentations), carried out at different loads ranging from 9.8 to 196 N. The crack lengths on the surface at each load were found to be decreased (8–12%) by glass treatment and the corresponding crack resistance values increased by about 17–20%. Both sintered and glass treated specimens showed rising trend in crack resistance values as the indentation load was increased. There was also a significant increase in the Weibull modulus value of crack resistance. Improved properties of glass treated sample were attributed to the formation of a relatively larger process zone surrounding the crack, crack arrest behavior due to the compressive stresses and the crack bridging phenomena. The compressive stresses were generated from the thermo-elastic properties mismatch: (a) between the glass and the ceramic in the glass infiltrated zone, and (b) the glass–ceramic composite layer and the ceramic substrate.